Who to blame for the economy's lack of oomph will be a crucial factor in the next election. The prime minister kept up the momentum in his speech on Thursday, blaming Labour's poor stewardship in the boom years for crippling debts, high oil prices for high inflation, and recession in the eurozone for lacklustre exports.

Claiming the OBR agrees that these three factors are the only ones that matter was too much for its boss, Robert Chote, who has struggled to burnish the image of his organisation as independent from its Whitehall paymaster's powerful influence.

At the autumn statement, Chote was accused by some of becoming Osborne's lackey. Many thought him complicit in bamboozling Ed Balls with projections of extra cash from the previously unannounced sale of 4G phone licences. Balls was wrong footed when Osborne declared that against all odds, he would meet his debt rule.

More importantly, with little explanation, the OBR downgraded crucial forecasts that allowed the chancellor to show many of his problems were temporary.

So Chote, a former director of the Institute for Fiscal Studies and Financial Times journalist, had a point to prove. His team, without much of a song and dance, has consistently recognised in its projections that cuts have consequences. In 2011-12 austerity reduced GDP by around 1.4%, they said. When Cameron said on Thursday, "They are absolutely clear that the deficit reduction plan is not responsible; in fact, quite the opposite", Chote had no choice but to react.

For Cameron, it is the second time in a month that a former IFS director has rebuked him for a cavalier attempt to improve the government's image.

The chair of the UK Statistics Authority, Andrew Dilnot, contradicted the prime minister when he said Britain was paying down its debts.

Reacting to a complaint by Labour, Dilnot pointed out that the stock of debt had risen from £811bn in 2010 when the coalition took office to £1.1tn at the end of last year.

The UK's debts are likely to still be rising in 2015 when voters go to the polls, making this a crucial battleground Cameron knows he must win.